1. Field of the Invention
The present invention relates to an inverter circuit, a backlight assembly, a liquid crystal display (“LCD”) having the same, and a method thereof. More particularly, the present invention relates to an inverter circuit that can detect an abnormal discharge at a high voltage, a backlight assembly having the inverter circuit, an LCD having the inverter circuit, and a method of detecting the abnormal discharge.
2. Description of the Related Art
LCDs have been required to have a lightweight structure, slim profile, low driving voltage, and low power consumption. Because LCDs are not self-luminous, a separate light source is needed. A cold cathode fluorescent lamp (“CCFL”) is widely used as the light source.
The CCFL is a fluorescent lamp that operates in the range of a normal glow discharge and is turned on/off by an AC high voltage.
Since the CCFL is not dependent on a preheating of filament, it has good vibration resistance compared with a hot cathode tube. Also, the CCFL can be made small in diameter and has a long lifetime.
Generally, an inverter circuit is used to generate the AC high voltage to turn on the CCFL. When an insulation failure occurs in an insulating material between a high voltage part and a ground due to the use of the AC high voltage, the CCFL is subject to high voltage discharge, such as a corona discharge, an arc discharge, etc. The high voltage discharge gradually carbonizes the insulating material, thereby causing a short circuit, a burning, and a smoking.
The insulation failure may be caused by bending or burring of electrodes, soldering crack, loss of insulating material, non-uniformity or deformation of the insulating material, and so on. Also, the insulation failure may be caused by degradation with time.
FIG. 1 is a circuit diagram of a conventional detector detecting an abnormal current caused by a high voltage discharge.
Referring to FIG. 1, a current detection resistor 200 is connected to a ground side of a secondary coil of an inverter transformer 900. The inverter transformer 900 boosts an AC voltage 94 and outputs AC high voltage 95 to the CCFLs 300. A differential circuit 45 having a condenser and a resistor detects a peak of a spike voltage occurring when an abnormal current caused by a high voltage discharge flows. A comparator 41 compares the detected peak voltage with a reference voltage 44. Through these operations, the abnormal current can be detected, and a control voltage 43 can be output from the voltage comparator 40.
Another related art will be described with reference to FIG. 2. FIG. 2 is a circuit diagram of a detector disclosed in Japanese Patent Laid-Open Publication No. 2002-341775. The detector of FIG. 2 detects a corona discharge that occurs in a transformer or a CCFL of a flat display device such as an LCD.
In the detector of FIG. 2, an inverter transformer is mounted on a printed board, and induction patterns are formed on a bottom surface of the inverter transformer and around a lamp. The detector detects the corona discharge using a voltage induced from the induction patterns.
The detector of FIG. 1 can detect the abnormal current caused by the high voltage discharge, but cannot detect it when the discharge occurs in a state that the high voltage part and the ground are in a high impedance state because the spike current is reduced.
Also, the detector of FIG. 2 can detect only the high voltage discharge around the inverter transformer and the lamp. That is, the detector cannot detect the high-voltage abnormal discharge that is caused when insulation failure occurs in the insulating material between another high voltage part and the ground.